Lead screw coupling

ABSTRACT

The disclosed embodiment of the present invention is a coupling for a lead screw and the like having four degrees of freedom and two degrees of constraint. The coupling is generally formed of three rectangular member, two of which have a central rectangular aperture for receiving another one of the members therein. The innermost member is pivotally supported within the central aperture of the intermediate member on one axis, and the intermediate member is pivotally supported within the central aperture of the outermost member on a second axis perpendicular to the first axis. The inner and outer peripheral surfaces of the members in assembled form are slightly spaced from one another to permit limited pivotal movement of the inner and intermediate members about their respective axes and to permit limited axial movement of the inner and intermediate members along their respective axes with respect to the outer member.

llnite States atent .l ones et al.

[54] LEAD SCREW COUPLING [72] Inventors: Derek Jones, Campbell, Calif.;Woodrow L. Hayes, Rye, N.l-l.

[73] Assignee: Singer-General Preclson, Inc., Binghampton, NY.

[22] Filed: Dec. 31, 1969 [21] Appl. No.: 889,585

[52] U.S.Cl ..248/1,64/l8 [51] ....A47g 29/00 [58] Field of Search..74/89.l5; 64/18; 248/184, 1

[56] References Cited UNITED STATES PATENTS 78,571 6/1868 Bronson..64/l8 1,058,878 4/1913 Lowndes... ..64/18 2,493,043 1/1950Stipsky..... 248/l84 2,605,072 7/1952 Klein et al. ..248/l84 2,643,5576/1953 Grove ..248/l84 3,404,859 10/1968 Chapman ..248/184 PrimaryExaminer-William F. ODea Assistant Examiner-Wesley S. Ratliff, Jr.

Attorney-Francis L. Masselle, William Grobman and Charles S. McGuire[57] ABSTRACT The disclosed embodiment of the present invention is acoupling for a lead screw and the like having four degrees of freedomand two degrees of constraint. The coupling is generally formed of threerectangular member, two of which have a central rectangular aperture forreceiving another one of the members therein. The innermost member ispivotally supported within the central aperture of the intennediatemember on one axis, and the intermediate member is pivotally supportedwithin the central aperture of the outermost member on a second axisperpendicular to the first axis. The inner and outer peripheral surfacesof the members in assembled form are slightly spaced from one another topermit limited pivotal movement of the inner and intermediate mem' bersabout their respective axes and to permit limited axial movement of theinner and intermediate members along their respective axes with respectto the outer member.

1 Claims, 3 Drawing Figures PATENTEBMWB I912 3,652,043

INVENTORS DEREK JONES BY WOODROW L.HAYES LEAD SCREW COUPLING Thisinvention relates generally to a coupling having four degrees of freedomand two degrees of constraint and in particular to such a coupling for alead screw and the like.

Various mechanical configurations require precise positioning andmovement of one part with respect to another part. For example, machinetools, X-Y plotters, and the like, in clude tables which are positionedby lead screws and other forms of actuators or positioning devices.Generally the table is guided and constrained to move in a desireddirection along a predetermined path, normally in straight lines, onrails. The table includes grooves having bearings therein for engagingthe rails. In those applications which require a high degree of accuracyin the positioning of, for example, a table, it is important to minimizethe reaction at the bearings created by any load which may be impartedthereto by the lead screw or actuator. In particular, the probleminvolves mounting the reacting part of the actuator in such a mannerthat the table is propelled only in the required direction of travel.

MOst conventional lead screw drives require extremely accurate alignmentbetween the axis of motion of the driven part and the lead screw axis.Accordingly, attempts are made to achieve exact straightness of thescrew and to eliminate any torsional effects thereon such thatstraightness can be main tained during operation. The obvious result isthat widely varying torque loads are reduced on the part to be displacedand wear on the tracks and guides is reduced. However, if the nut on thelead screw or the force transmitter is provided with at least fourdegrees of freedom and one degree of constraint, the lead screw need nothave such a high degree of accuracy. The present invention permits thelead screw to be significantly out-of-straight and misaligned to theaxis of motion without significantly effecting torque load or positionalaccuracy.

Accordingly, it is an object of the present invention to provide acoupling for a lead screw and the like having four degrees of freedomand two degrees of constraint.

Another object of the present invention is to provide a coupling whichis considerably less complicated, easier to manufacture, and less costlythan prior known couplers.

These and other objects, features and advantages of the presentinvention will be more fully realized and understood from the followingdetailed description, when taken in conjunction with the accompanyingdrawing, wherein:

FIG. I is an elevational view partly in section ofa preferred embodimentof the present invention;

FIG. 2 is a second view taken along line 2--2 of FIG. 1; and

FIG. 3 is a sectional view taken along line 33 of FIG. 1.

Like reference numerals throughout the various views of the drawingdesignate the same or similar elements.

With reference to the drawing, there is shown a coupling constructed inaccordance with the principles of the present invention which generallyincludes an inner member 10, an intermediate member 12, and an outermember 14. The inner member is generally rectangular in shape andincludes a central aperture 16 for receiving a lead screw or the liketherethrough. It should be understood, of course, that the inner member10 is not required to and does not engage the lead screw passingtherethrough. A plurality of mounting holes 18 are provided in themember 10 for securing the coupling to the force transmitter on theactuator, such as the nut on a lead screw. The member 10 is providedwith a pair of shafts 20 and 22 at opposite ends thereof. A common axispassing through the shafts 20 and 22 defines a first axis of rotationfor the coupling.

The intermediate member 12 is formed of a U" shaped member 24 and amember 26 which mates with the member 24 to form a generally rectangularaperture for receiving the member 10 therein. The member 24 is providedwith an aperture 28 for receiving the shaft 20 therein, and the member26 is provided with an aperture 30 for receiving the shaft 22 therein.The shafts 20 and 22 and the apertures 28 and 30 are machined to providea bearing fit therebetween. The member 24 is also provided with a pairof shafts 32 and 34. A common axis passing through the shafts 32 and 34defines a second axis of rotation for the coupling.

The outer member 14 is formed of a U shaped member 26 and a member 38mating therewith to define a central rectangular aperture for receivingthe intermediate member 12 therein. The member 36 is provided with anaperture 40 for receiving the shaft 32 therein and the member 38 isprovided with an aperture 42 for receiving the shaft 34 therein. Theshafts 32 and 34 and the apertures 40 and 42 are machined to provide abearing fit therebetween.

On a line perpendicular to the axis defined by shafts 20 and 22, theouter periphery of the member 10 is spaced from the inner periphery ofthe member 12 by an amount indicated with the reference numeral 44 inFIG. 2. The distance 44 is of a dimension to permit limited rotationalmovement of the member 10 with respect to the member 12 as indicated bythe dotted line outline of the member 10 in FIG. 2. As a result of thisspacing, member 10 can be rotated through an angle designated with thereference numeral 48. Along a line parallel to the axis defined by theshafts 20 and 22, the outer periphery of the member 10 is spaced fromeach side of the inner periphery of the member 12 by an amountdesignated with the reference numeral 50 in FIG. 3. As a result of thisspacing, the member 10 can move axially along the axis defined by theshafts 20 and 22 with respect to the member 12 by an amount equal totwice the distance 50.

Along a line perpendicular to the axis defined by the shafts 32 and 34,the outer periphery of the member 12 is spaced from the inner peripheryof the member 14 by an amount designated with the reference numeral 52in FIG. 3. The distance 52 is of a dimension to permit limitedrotational movement of the member 12 with respect to the member 14 asindicated by the dotted line outline of the member 12 which isdesignated with the reference numeral 54. As shown in FIG. 3, the member12 can be rotated through an angle designated with the reference numeral56 with respect to the member 14. Along a line parallel to the axisdefined by the shafts 32 and 34, the outer periphery of the member 12 isspaced from each side of the inner periphery of the member 14 by anamount designated with the reference numeral 58 in FIG. 2. Accordingly,the member 12 can move axially along the axis defined by the shafts 32and 34 by an amount equal to twice the distance 58 with respect to themember 14.

It can be readily appreciated from the above description that if a tableor the like structure is secured to the member 14, and a forcetransmitting member is secured to the member 10, the coupling willprovide four degrees of freedom and two degrees of constrainttherebetween. The four degrees of freedom include (1) rotation about theaxis defined by the shafts 20 and 22, (2) linear movement parallel tothe axis defined by the shafts 20 and 22, (3) rotation about the axisdefined by the shafts 32 and 34, and (4) linear movement parallel to theaxis of the aperture 16. Accordingly, any motion of the lead screw nutor force transmitting member along the axis of the aperture 16 will bereflected by corresponding movement of the member 14 in the samedirection.

It can also be readily appreciated from the above description and thedrawing that the coupling of the present invention is relativelyuncomplicated, does not present any difficult machining problems, and isrelatively inexpensive to construct. Fabrication of the individualmembers requires the simplest machining operations. Assembly of thecoupling is relatively simple, as can be readily appreciated from thedrawing. Assembly is accomplished by inserting the shaft 20 into theaperture 28 of the member 24 and attaching the member 26 to the member24 by suitable machine screws (not shown) while passing the shaft 22into the aperture 30. The outer member 14 is assembled onto theintermediate member 12 in the same manner. The inner member 10 can besecured to the force transmitting member of the actuator and the member14 can be secured to the driven part.

The invention claimed is:

1. Intermediate coupling structure for imparting linear motion from alead screw nut to a table, or the like, said structure comprising, incombination:

a an inner member having a central, circular aperture through which thelead screw may extend and means for fixedly securing the lead screw nutthereto;

b. an intermediate member having a central, rectangular aperture coaxialwith the aperture of said inner member;

c. means pivotally supporting said inner member in the aperture of saidintermediate member for rotation about and linear movement along a firstaxis with respect thereto;

d an outer member for fixed attachment to the table and having acentral, rectangular aperture coaxial with the apertures ofsaid innerand intermediate members;

e. means pivotally supporting said intermediate member in the apertureof said outer member for rotation about and linear movement along asecond axis, mutually perpendicular to said first axis and the axis ofsaid aperture;

f. the outer dimensions of said inner member relative to the dimensionsof the aperture of said intermediate member being such that saidrotation about and linear movement along said first axis are restricted;and

g. the other dimensions of said intermediate member relative to thedimensions of the aperture of said outer member being such that saidrotation about and linear movement along said second axis arerestricted.

1. Intermediate coupling structure for imparting linear motion from alead screw nut to a table, or the like, said structure comprising, incombination: a. an inner member having a central, circular aperturethrough which the lead screw may extend and means for fixedly securingthe lead screw nut thereto; b. an intermediate member having a central,rectangular aperture coaxial with the aperture of said inner member; c.means pivotally supporting said inner member in the aperture of saidintermediate member for rotation about and linear movement along a firstaxis with respect thereto; d. an outer member for fixed attachment tothe table and having a central, rectangular aperture coaxial with theapertures of said inner and intermediate members; e. means pivotallysupporting said intermediate member in the aperture of said outer memberfor rotation about and linear movement along a second axis, mutuallyperpendicular to said first axis and the axis of said aperture; f. theouter dimensions of said inner member relative to the dimensions of theaperture of said intermediate member being such that said rotation aboutand linear movement along said first axis are restricted; and g. theother dimensions of said intermediate member relative to the dimensionsof the aperture of said outer member being such that said rotation aboutand linear movement along said second axis are restricted.